Generally, a group resource allocation mechanism is a method of allocating resources to a plurality of users belonging to one group using a bitmap in order to reduce overhead attributed to a control message sent to a user equipment by a base station. In allocating resources to user equipments individually, this resource allocating method using the bitmap compresses and transmits such information as resource allocation position information (e.g., resource start offset, resource size, etc.), burst MCS (modulation and coding selection) level information and the like, thereby reducing overhead attributed to the control information transmission.
FIG. 1 is a diagram of a bitmap used by a group resource allocating method.
Referring to FIG. 1, a base station uses bitmaps to inform user equipments belonging to a group of resource allocation information. A user bitmap, which is a first bitmap, indicates whether a prescribed user equipment in a specific group is scheduled at a corresponding timing point. Each bit of the user bitmap corresponds one-to-one to user equipments belonging to a group. In FIG. 1 (a) and FIG. 1 (b), users up to 6 can belong to one group. If each bit is represented as ″, it indicates a user schedule in a current frame (i.e., a user having a resource allocated thereto). In the nth frame shown in FIG. 1 (a), 1st, 2nd, 4th and 6th users are scheduled. A user equipment can be aware of its position order in a group by acquiring information for a user bitmap. In this case, the user bitmap is received from a base station when it is added to the corresponding group. A resource allocation bitmap indicates resource allocation information (modulation & coding selection (MCS) and resource size) of the scheduled users.
In FIG. 1 (a) and FIG. 1 (b), information on one user equipment is represented as 3 bits. Since total 4 users are scheduled in the nth frame, a size of a resource allocation map becomes 12 bits. Referring to FIG. 1 (b), since total 5 users are scheduled in the (n+p)th frame, a size of a resource allocation map includes total 15 bits.
Group control information is the information used in configuring and allocating a resource for at least one user (or user equipment) within one user group. Two kinds of operations are required for group scheduling as follows. First of all, an operation of allocating one user to one group is required. In order to add one user to one group in downlink (DL) or uplink (UL), a base station sends a group configuration MAC management message and a group configuration A-MAP IE to a user equipment. Secondly, an operation of allocating resources to users within one group is required. In order to allocate resources to at least one or more users within one group, a base station transmits a DL/UL group resource allocation A-MAP IE to a user equipment. In this case, the DL/UL group resource allocation A-MAP IE is included in a user-specific resource assignment within A-MAP region. The DL/UL group resource allocation A-MAP IE includes a bitmap which indicates scheduled users or signals resource allocation, modulation & coding scheme (MCS) and a resource size.
Table 1 shows DL/UL group resource allocation A-MAP IE according to a related art.
TABLE 1Size inSyntaxbits*Description/NotesA-MAP IE Type[4]A-MAP IE types distinguish between UL/DL, SU/MU,OL/CL MIMO operation, persistent/non-persistent allocation,basic/extended IEs including GRAResource Offset[6] [8]Indicates starting LRU for resource assignment to thisgroupACIDTBDRequested for explicit assignment of a single ACIDgroup. Implicit cycling of ACIDs needs not to be usedaccording to IEEE 802.16e from initial ACID value.HARQ Re TxTBDIndicates whether this group resource allocation IE is forIndicatorHARQ retransmission or initial transmission.User Bitmap[2] [5]Size of user bitmap: This may be unnecessary if a userSizebitmap size is included in configuration message/A-MAP IE.User BitmapVariableThis is a bitmap indicating a scheduled user in onegroup. Size of this bitmap is equal to a user bitmap size.ResourceTBDAttributes required for decoding MCS group type,Allocationpacket/resource size type information or resource allocationBitmapbitmapdescriptorResourceVariableIndicates MCS/resource size for each scheduled user.AssignmentBitmapPaddingVariablePadding to reach byte boundaryMCRC[16]16 bit masked CRC
Referring to Table 1, when a specific group is assigned to one user equipment or a specific user equipment is deleted from an assigned group, it is able to use A-MAP (group configuration A-MAP IE) or a MAC management message (group configuration MAC management message).
Table 2 shows formats of information elements (IEs) included in A-MAP IE or MAC management message for group configuration.
TABLE 2Size inSyntaxbits*Description/NotesManagement4messageType/A-MAPIE TypeGroup ID5Start frameIndicates that 1st group resource allocationA-MAP IE is transmitted after transmissionof this message. The unit is the number offrame.MCS/resourceTBDsize set IDUser Bitmap5indexInitial ACIDTBDIndicates a start of ACID used for groupresource allocationN_ACIDTBDIndicates the number of ACID used forgroup resource allocationCH indicator1Indicates whether a default MAC header ofMPDU is a generic MAC header or acompact MAC header.0b0: GenericMAC header0b1: CompactheaderFlow ID4Indicates a flow ID included in this group.PaddingVariablePadding to reach byte boundaryMCRC[16] 16 bit masked CRC
Referring to Table and Table 2, if a group is configured using A-MAP for user equipments, it is necessary to define an additional A-MAP IE type for the delivery of information having low frequency of occurrence. Moreover, since modulation and coding scheme (MCS) used in transmitting the A-MAP is lower than that used in transmitting a message, if a size of information for the group configuration is greater than that of information of general resource allocation A-MAP IE, the A-MAP for the group configuration occupies more resources.
Meanwhile, in case of using a message type, information can be transmitted in a manner of occupying relatively small resources if MCS higher than that of A-MAP IE is used. Moreover, when there is a DL MPDU (MAC protocol data unit) which is to be transmitted to a user equipment having a good channel, if there is a spare resource to include a group configuration message, a base station is able to send the group configuration message by concatenating the DL MPDU and the group configuration message with each other.
Yet, when a channel status of a user equipment is poor, if a group configuration message needs to be sent as a single message type, since a basic A-MAP IE indicating allocation information of message should be transmitted, an additional resource is occupied. Therefore, this case may cause a problem of occupying more resources than those for the case of configuring a group using A-MAP IE.
Thus, in order to add/delete a user equipment to/from a group, a base station sends a group configuration MAC message including information related to the addition and deletion to the corresponding user equipment. Having received the group configuration MAC message, the user equipment receives an assignment to a group based on the information included in the message. A bit size used for a MAC message for the group configuration is explained as follows. First of all, for the group addition, it is able to use 26 bits (including group ID, allocation periodicity, user bitmap information, HARQ information (initial ACID, N ACID, etc.), burst size information, resource allocation information and the like). For the group deletion, it is able to use 5 bits (1-bit deletion flag, 4-bit FID). For the group addition or the group deletion, there is 83-bit overhead (GMH+FEH: 3˜4 bytes, CRC (cyclic redundancy checking): 2 bytes, RLC/Security (PN in IEEE 802.16m system): 3 bytes, MAC message type: 1 byte, Padding to MAC message: 3 bits)) in common.
Thus, when the group deletion is performed, 83-overhead (16-times overhead) is generated to send 5-bit information. However, there is a problem that the unnecessary overhead considerably lowers efficiency of resource use.